Microstructural and mechanical properties of polycrystalline Ni78Al22 alloy prepared by directional solidification at three growth rates of 18, 60 and 108mm/h were studied. After directional solidification, the microstructure consisted of coarse columnar γ'(Ni3Al) grains, which solidified directly from the melt, fine γ' grains formed from primary γ-phase (Ni-based solid solution) and γ' nanoparticles formed in the γ channels surrounding fine and coarse γ' grains. Volume fraction of the γ'-phase increased from 70 to 75vol% with decreasing growth rate from 108 to 18mm/h. The highest room temperature tensile ductility was measured in the specimens with the highest volume fraction of the γ'-phase, which was prepared at the lowest growth rate of 18mm/h. After fracture the proportion of the dislocation density in the gauge section to that in the heads was an order of magnitude higher in the specimens showing the highest ductility than that in the specimens showing the lowest ductility. High values of room temperature ductility result from an intensive multiplication of dislocations during tensile deformation.

Microstructural Analysis and Mechanical Properties of Polycrystalline Ni-Rich Ni3Al Alloy Prepared by Directional Solidification. Kursa, M., Malcharcziková, J., Pešička, J., Vodárek, V., Hyspecká, L.: Kovove Materialy, 2008, 46[6], 351-9